And the city with the world's worst air quality is…

Nope, it's not Beijing.

According to data released by the World Health Organization, there are dozens of cities where the air is more packed with nitrogen oxide, soot, and ozone molecules than in Beijing.

China's abysmal air quality often garners negative media attention (including here on but the data shows that the world's worst air pollution hovers over Ahwaz, Iran.

The average  level of large pollutant particles (PM10) in Ahwaz is a staggering 372, far above the global average of 71.

Ulaanbaatar, Mongolia's capital, is number two with an average of 279 PM10.

Beijing is far behind the leading dirty air pack, with PM10 levels of 121.

In an article today for Slate Magazine, John Upton discusses the rankings in detail and the horrific air quality in the city he now calls home, New Delhi.  Air pollution is the number five killer in India.